hiya! there's 2 separate issues to understand here:
1) someone in your group needs to be able to host games by forwarding port 6112 in their router. (this is the correct guide to follow: http://en.war2.ru/hosting
) once that's done, other people on the server should be able to join games hosted by that person. if other people on the server
(not your friends) still can't join the games then the port forwarding didn't work correctly & we'll need to do additional troubleshooting to fix it. once it's confirmed that hosting is set up correctly you can move on to the next issue.
2) it's common for people on the same connection to be unable to play in the same game together, even if one or both are able to host & play with other people. you can fix this by using a VPN on one of the computers to give it a new IP address which will bypass the problem. also, whoever is able to host games should NOT use the VPN, so if you & your brother are on the same connection and you set up port forwarding for your pc, then your brother needs to be the one to use the VPN. here's a quick guide for using the free VPN tunnelbear: http://en.war2.ru/support/multiple-people-on-same-network-have-high-latency-lag/
(scroll down to where it says "Workaround – Using a VPN")
let us know if this helps!